Dell EMC SmartFabric OS10 User Guide Release 10.5.0

OS10 supports 4-byte AS number configurations by default. The 4-byte support is advertised as a new BGP capability - 4-BYTE-AS, in the OPEN message. A BGP speaker that advertises 4-Byte-AS capability to a peer, and receives the same from that peer must encode AS numbers as 4-octet entities in all messages.

If the AS number of the peer is different, the 4-byte speaker brings up the neighbor session using a reserved 2-byte ASN, 23456 called AS_TRANS. The AS_TRANS is used to interop between a 2-byte and 4-byte AS number.

Where the 2-byte format is 1 to 65535, the 4-byte format is 1 to 4294967295. You can also enter AS numbers using the dotted decimal format. For example, you can enter 0.123.